We propose to establish a Rare Disease Clinical Research Center (RDCRC) at the Children's National Medical Center (CNMC) in Washington, D.C. The RDCRC will draw support from both the Pediatric General Clinical Research Center at CNMC/Georgetown University Medical Center (GUMC) as well as its Mental Retardation and Developmental Disabilities Research Center (MRDDRC). The unifying clinical theme of the RDCRC is the study of urea cycle disorders (UCD). This RDCRC will consist of a network of 5 academic institutions, each of which has GCRC/MRDDRCs [CNMC/GUMC, Children's Hospital of Philadelphia, Vanderbilt University, Baylor Medical Collage and University of California at Los Angeles]. The proposed RDCRC will comprise a multidisciplinary team of 10 investigators in the following specialties: Genetics, Metabolism, Developmental Pediatrics, Clinical Pharmacology, Neurology, Psychology, Biostatistics, and Neuroimaging. Mark L. Batshaw, M.D., the Director of the CNMC MRDDRC, will serve as Principal Investigator; and Mendel Tuchman, M.D., Director of the PCRC at CNMC, will serve as Co-Director. The primary goals of the RDCRC are to: 1) Establish a registry and nation-wide network of regional centers for the diagnosis, treatment and clinical research in UCD; 2) Conduct a longitudinal study to determine the natural history of UCD; 3) Conduct a clinical trial of an investigational new drug (IND), N-carbamyI-L-glutamate, for treatment of these disorders; 4) Conduct a demonstration/pilot project to develop a novel method for measuring in vivo ureagenesis in UCD that will be important for diagnosis and classification of patients and for evaluation of treatment efficacy; 5) Train graduate students, pediatric residents, clinical fellows and junior faculty members in the field of inborn errors of metabolism; and 6) Develop and maintain UCD website content that will: (a) include guidelines for health care providers regarding diagnosis and treatment; (b) provide information to the lay public regarding consultation and treatment at major centers; and (c) provide links to recent scientific literature for interested investigators. This initiative will be undertaken in close. collaboration with the National Urea Cycle Disease Foundation (NUCDF), the leading public advocacy organization for this group of diseases.